Planting, flea beetles and children

Late May is a busy time in Front Range vegetable gardens. With Memorial Day weekend rains (3 inches in my Denver garden), weeds are growing but easy to pull. Soil is moist for transplanting tomatoes and other warm season plants into the garden. It is also the time to direct-seed warm soil requiring plants like squash, beans, corn and cucumbers.

A visit to the West Washington Park community garden reminded me of several things. The first was how much the heat island effect of city centers has on advancing the season. Their gardens are about a week ahead of gardens in the outer parts of Denver due to the warmer temperature.

Second, early season insect pests are becoming active, foremost among them flea beetle. Germinated beans were already showing holes (photo above left) and upon closer examination, the shiny hopping beetles were present (palestriped flea beetle photo below).

Not only beans but tomato family and cabbage family plants are attacked among other vegetables. Watch young seedlings closely and take action before damage becomes too extensive. While mature plants can withstand some 10 to 20 percent loss of leaf tissue with no adverse affect, seedlings are another matter.

Trap crops such as radish are one good idea. Diatomaceous earth is an effective repellent, and several insecticides including the bio-derived spinosad are effective. Weekly reapplications are often necessary as new plant growth will be unprotected and insects are very mobile. For more photos and control recommendations, see the Colorado State University Extension Flea Beetles fact sheet.

The third reminder I received from my visit is to involve children in your vegetable gardening efforts. Now that school is out, choose age-appropriate garden activities for children and youth, whether they are yours or your neighbors. They will be the richer for early involvement in the garden and receiving the benefit of your presence in their lives.

Photo credits:
Flea beetle damage on bean seedlings, Carl Wilson
Palestriped flea beetle close up, Frank Peairs, Colorado State University, Bugwood.org
Children’s toys among beet seedlings, Carl Wilson

Raspberry pruning

Red raspberries are very hardy and grow well along the Front Range. Black and purple raspberries do better in milder climates like the fruit producing areas on the West Slope.

While raspberry clumps are perennial, individual raspberry canes should be removed after they have fruited once. In practice, this means that canes should be pruned out after either their first or second year. The trick is to know which year to prune.

The raspberries you have may be either summer (June) fruiting varieties, or fall bearing plants that produce a late summer/fall crop. Summer bearers flower and bear fruit on canes that grew the previous year. Once they fruit, those canes won’t produce a crop again and should be removed. Recommended summer bearing varieties are Latham, Boyne, Laura and Honey Queen.

Fall varieties bear fruit on new growth produced in the summer. Those canes will produce a light early summer crop the next summer. After that, the canes should be removed. Fall bearing canes can be cut down to the ground in early spring if an early crop of fruit isn’t wanted. Fall bearing varieties include Heritage, September Red, Fall Red, Red Wing, Amity, Pathfinder, Trailblazer, Plainsman, Perrone’s Red, Caroline, Autumn Bliss, Goldie and Anna.

Tomatoes love night heat

Last post discussed heirloom and modern tomato varieties and adaptation. Warmer gardening situations, particularly at night, will help both be productive.

Grow tomatoes in full sun or choose a hot south or west exposure. If there is masonry nearby that can absorb heat by day and radiate it at night, it’s often for the better in our high elevation climate. Examples of these heat sinks are walls [left photo with lattice], pavement and rock.

Some gardeners have placed large rocks between tomato plants to act as “warming stones” [photo right] at night. The nice thing about this idea is that they can be removed if necessary during 90 to 100 degree F mid-summer heat when nights are warm and re-introduced in late summer as weather cools.

People who succeed with longer days to harvest varieties usually garden in the center of a city (heat island), locate their garden in a warm exposure and have heat-retaining pavement or walls near their tomatoes. A warmer than average microclimate at night is the reason behind their success at 5280’, mile-high Denver elevation.

Gardeners in Castle Rock (6200’ elevation) and Colorado Springs (6000 – 7200’) will have shorter growing seasons and more difficulty growing long season tomatoes. Carefully selected exposure, microclimate and use of season extenders such as Wall O’Water®, Season Starter™ and Kozy Coat™ [See May 3rd post] are even more important in these situations. Higher elevation foothill gardeners are more challenged. Mountain gardeners with very short growing seasons should consider growing warm season vegetables in greenhouses.

Have a favorite location or microclimate for your tomatoes? Discuss it by clicking comment below to let us know.

[Tomatoes on brick wall and warming rock photos – Carl Wilson]

Tomato variety choices

There are hundreds of tomato varieties and your garden center probably stocks ten to twenty. Which one is right for you?

In recent years, heirloom tomatoes have been in vogue. Unfortunately some of these varieties require a relatively large number of days to harvest. Examples are Purple Cherokee (85), Yellow Brandywine (90) ["potato leafed" variety photo below left] and Beefstake (85 days).

In Denver the average growing season is 155 days (May 10 to Oct 11). In some years like 2007 the growing season is short, only 123 days (June 8 to October 8). In addition, there were only 81 days with night temperatures greater than 55 degrees F. Why is this last tidbit important?

Tomatoes require warm night temperatures for growth. Night temperatures below 55 degrees F tend to slow and shut down growth. Depending how cold the nights, growth may take days to resume. This loses you valuable time in the race to tally growing days for maturity.

The high and dry environment of Colorado’s Front Range creates a summer climate that has warm days (80 or 90 degrees F) and thirty degree cooler nights due to radiational cooling (50 or 60 degrees F). Summers are very comfortable for people but not as conducive to growing heat-loving crops like tomatoes that prefer the warm nights of the Midwest and Eastern U.S. where the humidity prevents heat loss at night.

The other factor that decreases yield of tomato fruit is the arrangement of the flower. Varieties that do well here tend to have reproductive parts tucked well into the staminate cone in the middle of the flower. When reproductive parts protrude to or beyond the cone opening, they dry in our low humidity and wither before they pollinate. Tomatoes bred in New Jersey, Florida and other places in the East often don’t yield well here for this reason.

Modern tomato varieties tend to require a smaller number of days to harvest. Many cherry types are 50 to 60. ‘Early Girl’ and derivations are in the low 60’s. ‘Celebrity’ is 70. The ‘Boy’ types are in the low 70’s. My advice is to choose a variety requiring 80 or fewer days to harvest.

Next post, microclimate location and tomato success.

Tomato photos credit: Carl Wilson

Season extenders for early birds

The Front Range’s mid-May average last frost date means it’s still too early to plant warm season vegetables such as tomatoes, eggplant, peppers and squash. Or is it?

Transplanting vegetables instead of direct garden seeding is one way of extending the growing season. You or your greenhouse grower typically start seed indoors 6 to 8 weeks before plants can be transplanted to the garden. Coddling plants inside when outdoor weather is still too cold gains you valuable “days to maturity” necessary for longer season vegetables to achieve the goal of producing fruit.

Another tool is in-garden season extenders. Products include Wall O’Water® (being filled with water right), Season Starter™ and Kozy Coat™. These plastic cones with water channels in the side use sound principles of physics to keep plants warm. The water absorbs heat from our abundant sunshine by day and releases it at night. Regulate the temperature in the cone by nudging the top open to ventilate on warm days and closed during cloudy weather and cold nights. Plant as much as a month early in April with these devices.

Remember that the mid-May average last frost date is just an average and can vary a month either direction. The snowy garden photo left was taken in Denver on May 24, 2002. Unless season extenders are used to minimize risk, playing the last frost average too closely can trip-up gardeners. This is why some risk-adverse gardeners don’t plant tomatoes until Memorial Day.

Keep in mind that extending the season is much more than frost protection provided by a sheet thrown over plants. It’s about keeping plants warm at night. Tomatoes in particular are markedly set back by nights cooler than 55 degrees F. They simply stop growing even though they haven’t frozen.

While growth is halted by night temperatures in the high thirties or forties, you lose valuable days and weeks in the quest for the necessary days to maturity in our short growing season. It takes plants days and even a week to resume active growth even when night temperatures warm.

Commercial plastic cones with water channels or home-rigged plastic milk jugs filled with water and circled around plants (photo with bean plant right) are valuable in extending our growing season. If you’re itching to plant early, season extenders are a must.

See the CSU Extension Garden Note on Frost Protection and Extending the Garden Season for more information.